Hydrogen gas generator

ABSTRACT

The invention is a hydrogen generator with a liquid reservoir, a reaction area, a byproduct containment area and a hydrogen containment area within a housing. A liquid from the liquid reservoir can react within the reaction area to produce hydrogen gas and byproducts, which flow to the byproduct containment area, and hydrogen gas passes into the hydrogen containment area and is released from the housing through a hydrogen outlet as needed. The liquid reservoir and the reaction area are each within a container made of a liquid impermeable material, the byproduct containment area is within a flexible container made of a hydrogen permeable, liquid impermeable material, and the hydrogen containment area is within a flexible container made of a hydrogen impermeable material. The byproduct containment area is in a volume exchanging relationship with one or both of the liquid reservoir and the reaction area.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application No.61/502,030, filed Jun. 28, 2011.

FIELD OF THE INVENTION

This invention relates to a hydrogen gas generator, particularly ahydrogen generator for a fuel cell system.

BACKGROUND

Interest in fuel cell batteries as power sources for portable electronicdevices has grown. A fuel cell is an electrochemical cell that usesmaterials from outside the cell as the active materials for the positiveand negative electrode. Because a fuel cell does not have to contain allof the active materials used to generate electricity, the fuel cell canbe made with a small volume relative to the amount of electrical energyproduced compared to other types of batteries.

Fuel cells can be categorized according to the types of materials usedin the positive electrode (cathode) and negative electrode (anode)reactions. One category of fuel cell is a hydrogen fuel cell usinghydrogen as the negative electrode active material and oxygen as thepositive electrode active material. When such a fuel cell is discharged,hydrogen is oxidized at the negative electrode to produce hydrogen ionsand electrons. The hydrogen ions pass through an electricallynonconductive, ion permeable separator and the electrons pass through anexternal circuit to the positive electrode, where oxygen is reduced.

In some types of hydrogen fuel cells, hydrogen is formed from a fuelsupplied to the negative electrode side of the fuel cell. In other typesof hydrogen fuel cells, hydrogen gas is supplied to the fuel cell from asource outside the fuel cell. A fuel cell system can include a fuel cellbattery, including one or more fuel cells, and a hydrogen source, suchas a fuel tank, a hydrogen tank or a hydrogen generator. In some fuelcell systems, the hydrogen source can be replaced after the hydrogen isdepleted. Replaceable hydrogen sources can be rechargeable ordisposable.

A hydrogen generator uses one or more reactants containing hydrogen thatcan react to produce hydrogen gas. The reaction can be initiated invarious ways, such as hydrolysis and thermolysis. For example, tworeactants can produce hydrogen and byproducts. An accelerator and/or acatalyst can be used to increase the rate of reaction or catalyze thereaction. When the reactants react, reaction products including hydrogengas and byproducts are produced.

In order to minimize the volume of the hydrogen generator, volume thatis initially occupied by the reactants can be used to accommodatereaction products as the reactants are consumed by arranging thecomponents of the hydrogen generator in a volume exchangingconfiguration. As reactants are consumed, volume that they had occupiedis simultaneously made available to contain reaction products.

The hydrogen gas is separated from byproducts and unreacted reactants,and the gas exits the hydrogen generator and is provided to the fuelcell battery. Various means for separating the hydrogen gas are known,including porous filters to separate solids from the hydrogen gas andgas permeable, liquid impermeable membranes to separate the hydrogen gasfrom liquids. Such means of separating the hydrogen gas can becomefilled or blocked by solids, thereby restricting or blocking the flow ofhydrogen gas so the gas cannot exit the hydrogen generator.

It is desirable to provide a hydrogen generator capable of supplyinghydrogen gas to a fuel cell stack with improved effectiveness andreliability of the separation of hydrogen gas from liquids and solidswithin the hydrogen generator. The hydrogen generator is advantageouslyless susceptible to internal restrictions or blockages that can impedethe separation and release of the hydrogen gas. It is further desirablethat the hydrogen generator have excellent reliability, safety, volumeefficiency and a simple design that is easily manufactured at a lowcost.

SUMMARY

The above objects are met and the above disadvantages of the prior artare overcome by a hydrogen generator and a fuel cell system as describedbelow.

Accordingly, one aspect of the present invention is hydrogen generatorincluding a housing; a liquid reservoir within the housing and includinga liquid reactant container, made of a liquid impermeable material, andcontaining a liquid including a first reactant; a reaction area withinthe housing and including a reaction container, made of a liquidimpermeable material, and within which the first reactant reacts toproduce hydrogen gas and byproducts; a byproduct containment area withinthe housing and including a flexible byproduct container, made of ahydrogen permeable, liquid impermeable material through which solids andliquids cannot pass but through which hydrogen gas can pass; a hydrogencontainment area within the housing and including a flexible hydrogengas container, made of a hydrogen impermeable material, and configuredto contain hydrogen gas from the byproduct containment area; and ahydrogen outlet from the hydrogen containment area through the housing.The byproduct containment area is in a volume exchanging relationshipwith at least one of the liquid reservoir and the reaction area.

The hydrogen generator can include one or more of the followingfeatures:

-   -   the byproduct container material is an elastic material, capable        of stretching and contracting;    -   the byproduct container material includes a fluoropolymer; the        fluoropolymer can include an expanded fluoropolymer; the        fluoropolymer can include a polytetrafluoroethylene or a        polytetrafluoroethylene derivative;    -   the hydrogen containment container material includes a        metallized polymer film or a metal-polymer composite film;    -   a catalyst configured to catalyze the reaction of the first        reactant is initially contained within the reaction area;    -   a second reactant is initially contained within the reaction        area; the second reactant can include a chemical hydride,        preferably a metal hydride, more preferably sodium borohydride;        the second reactant can be a solid; a solid pellet can include        the second reactant; the solid pellet can further include a        binder;    -   the hydrogen generator includes an accelerant that is capable of        providing an increased rate of reaction; the accelerant can        include an acid;    -   the reaction container includes an outlet through which hydrogen        gas and byproducts can exit to the product containment area;    -   the hydrogen generator further includes a pump configured to        pump the liquid from the liquid reservoir to the reaction area;        the pump can be disposed within the hydrogen generator; and    -   a liquid dispersion device is disposed within the reaction        chamber.

Another aspect of the invention is a fuel cell system including a fuelcell stack and a hydrogen generator as described above. The hydrogengenerator can be removable for the rest of the fuel cell system.

These and other features, advantages and objects of the presentinvention will be further understood and appreciated by those skilled inthe art by reference to the following specification, claims and appendeddrawings.

Unless otherwise specified, the following definitions and methods areused herein:

-   -   “effluent” means non-gaseous reaction products and unreacted        reactants, solvents and additives;    -   “expand” when used in describing a filter means for the filter        material to simultaneously increase in volume, increase in        porosity and decrease in density and pertains only to the        material of which the filter is made;    -   “initial” means the condition of a hydrogen generator in an        unused or fresh (e.g., refilled) state, before initiating a        reaction to generate hydrogen;    -   “volume exchanging relationship” means a relationship between        two or more areas or containers within a hydrogen generator such        that a quantity of volume lost by one or more of the areas or        containers is simultaneously gained by one or more of the other        areas or containers; the volume thus exchanged is not        necessarily the same physical space, so volume lost in one place        can be gained in another place.

Unless otherwise specified herein, all disclosed characteristics andranges are as determined at room temperature (20-25° C.).

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic cross-sectional drawing of a hydrogen gasgenerator in an initial state; and

FIG. 2 is a schematic cross-sectional drawing of the hydrogen gasgenerator in FIG. 1 in a subsequent state.

DESCRIPTION

A hydrogen generator according to an embodiment of the present inventionincludes reactants that can react to produce hydrogen gas. One or morereactants are contained in a liquid stored in a reservoir within thehousing. The liquid is essentially stable within the reservoir. Theliquid is transferred to a reaction area, where the reactants react. Ifall reactants are contained in the liquid, reaction can be initiated byone or a combination of methods, such as contact with a catalyst,changing the pH of the liquid or heating the liquid. Alternatively, atleast one reactant can be located elsewhere in the hydrogen generator.For example, if the other reactant(s) are contained in another liquid,the other liquid can be stored in another reservoir and be transferredto the reaction area to react with the first liquid, or the other liquidcan be stored in the reaction area. If the other reactant(s) are insolid form, they can be stored within the reaction area.

When the reactants react, hydrogen gas and byproducts are produced inthe reaction area and flow to the byproduct containment area. Someunreacted reactants can be carried to the byproduct containment area bythe flow of hydrogen gas and byproducts. To minimize the amount ofunreacted reactants in the byproduct containment area, a screen or othertype of filter can be located near the exit from the reaction area tohelp retain particles of solid reactants within the reaction area, oradditional liquid reactant can be transferred to the byproductcontainment area or an intermediate area to react with unreactedreactants carried from the reaction area. Unreacted reactants can alsocontinue to react within the byproduct containment area. A catalyst oraccelerant can be included in the byproduct containment area to promotereaction of any unreacted reactants present.

During use of the hydrogen generator, reactants stored in reservoirs andreaction area are depleted so less volume is required for those areas.If the containers for those areas can become smaller as the contents aredepleted (e.g., by collapsing or shrinking), the volume vacated by thoseareas becomes available to accommodate the increasing volume of thebyproduct containment area, which has an expanding container. Thebyproduct container is made of a gas permeable and liquid impermeable toallow hydrogen gas but not liquids and solids in the byproductcontainment area to pass therethrough, so that the gas is separated fromthe liquids and solids. Gas passing through the byproduct container iscollected within the hydrogen containment area, which is containedwithin a container made of a hydrogen impermeable material untilreleased through an outlet through the hydrogen generator housing.

A volume exchange between the product containment area and at least oneof the liquid reservoir and the reaction area provides good volumeefficiency, so that the total volume of the hydrogen generator does nothave to be large enough to hold the sum of the volumes of the reactantsplus byproducts, and the hydrogen generator can be made as small aspossible.

Because the hydrogen containment area is essentially hermetically sealedwithin the hydrogen gas container, the hydrogen gas container canprovide improved resistance to hydrogen gas leakage from the hydrogengenerator, the housing may not have to be made of a hydrogen impermeablematerial, and the housing does not necessarily have to be hermeticallysealed. This allows for the use of many different types of materials forthe housing, allows the use of other housing sealing methods, and cansimplify the hydrogen generator manufacturing process. Materials can beselected based on other desirable properties such as low cost, highstrength, heat resistance, moldability, workability, and so on withoutregard to hydrogen impermeability. Examples of materials that may beconsidered include plastics (e.g., polyphenylene sulfides such as RYTON®(Boedeker Plastics), polysulfones such as polyphenylsolfone, polysulfoneand polyethersulfone, glass reinforced plastics such as glass fiberreinforced polyacrylamides such as IXEF® (Solvay Advanced Polymers),ceramics (e.g., silicon carbide, kaolinite and glass) and combinationsthereof (e.g., metal lined plastic). The container can also be closedusing fasteners, such as screws, rivets, nuts and bolts, clips, clamps,and so on, which may not be suitable if a hermetic seal is required, andthe use of additional sealants, caulking, gaskets and so on may not benecessary. The container can also be closed using methods that may becapable of providing a hermetic seal, but without the process controls,etc., that may be necessary to insure the seal is hermetic. A separatecontainer for the hydrogen containment area also facilitates reuse ofthe hydrogen generator, since the contents of a used hydrogen generatorcan be readily removed and replaced.

Hydrogen gas can be provided by the hydrogen generator to a hydrogenconsuming apparatus such as a hydrogen fuel cell stack. The hydrogenconsuming apparatus and the hydrogen generator can be incorporated intoa system that includes controls for controlling the transfer of liquidfrom the liquid reservoir to the reaction area of the hydrogengenerator.

The hydrogen generator can use a variety of reactants that can react toproduce hydrogen gas. Examples include chemical hydrides, alkali metalsilicides, metal/silica gels, water, alcohols, dilute acids and organicfuels (e.g., N-ethylcarbazole and perhydrofluorene).

An alkali metal silicide is the product of mixing an alkali metal withsilicon in an inert atmosphere and heating the resulting mixture to atemperature of below about 475° C., wherein the alkali metal silicidecomposition does not react with dry O₂. Such alkali metal silicides aredescribed in US Patent Publication 2006/0002839. While any alkali metal,including sodium, potassium, cesium and rubidium may be used, it ispreferred that the alkali metal used in the alkali metal silicidecomposition be either sodium or potassium. Metal silicides including aGroup 2 metal (beryllium, magnesium, calcium, strontium, barium andradium) may also be suitable. In an embodiment, sodium silicide canreact with water to produce hydrogen gas and sodium silicate, which issoluble in water.

A metal/silica gel includes a Group 1 metal/silica gel composition. Thecomposition has one or more Group 1 metals or alloys absorbed into thesilica gel pores. The Group 1 metals include sodium, potassium,rubidium, cesium and alloys of two or more Group 1 metals. The Group 1metal/silica gel composition does not react with dry O₂. Such Group 1metal/silica gel compositions are described in U.S. Pat. No. 7,410,567B2 and can react rapidly with water to produce hydrogen gas. A Group 2metal/silica gel composition, including one or more of the Group 2metals (beryllium, magnesium, calcium, strontium, barium and radium) mayalso be suitable.

As used herein, the term “chemical hydride” is broadly intended to beany hydride capable of reacting with a liquid to produce hydrogen.Examples of chemical hydrides that are suitable for use in the hydrogengenerating apparatus described herein include, but are not limited to,hydrides of elements of Groups 1-4 (International Union of Pure andApplied Chemistry (IUPAC) designation) of the Periodic Table andmixtures thereof, such as alkaline or alkali metal hydrides, or mixturesthereof. Specific examples of chemical hydrides include lithium hydride,lithium aluminum hydride, lithium borohydride, sodium hydride, sodiumborohydride, potassium hydride, potassium borohydride, magnesiumhydride, calcium hydride, and salts and/or derivatives thereof. In anembodiment, a chemical hydride such as sodium borohydride can react withwater to produce hydrogen gas and a byproduct such as a borate. This canbe in the presence of a catalyst, heat, a dilute acid or a combinationthereof.

Chemical hydrides can react with water to produce hydrogen gas andoxides, hydroxides and/or hydrates as byproducts. The hydrolysisreaction may require a catalyst or some other means of initiation, suchas a pH adjustment or heating. Chemical hydrides that are soluble inwater can be included in the liquid reactant composition, particularlyat alkaline pH to make the liquid sufficiently stable. The reaction canbe initiated by contacting the chemical hydride solution with acatalyst, lowering the pH (e.g., with an acid), and/or heating. Chemicalhydrides can be stored as a solid, and water can be added. A catalyst oracid can be included in the solid or liquid composition.

One or more catalysts can be used to catalyze the hydrogen producingreactions. Examples of suitable catalysts include transition metals fromGroups 8 to 12 of the Periodic Table of the Elements, as well as othertransition metals including scandium, titanium, vanadium, chromium andmanganese. Metal salts, such as chlorides, oxides, nitrates and acetatescan also be suitable catalysts.

The rate of hydrogen generation can be controlled in a variety of ways,such as controlling of the rate at which liquid is transported to thereaction area, adjusting the pH, and making thermal adjustments. Therate of hydrogen generation can be controlled to match the need forhydrogen gas. A control system can be used for this purpose, and thecontrol system can be within or at least partially outside the hydrogengenerator.

Additives can be used for various purposes. For example, one or moreadditives can be included with a solid reactant as a binder to hold thesolid material in a desired shape or as a lubricant to facilitate theprocess of forming the desired shape. Other additives can be includedwith a liquid or solid reactant composition to control pH. Suchadditives include but are not limited to acids (e.g., hydrochloric,nitric, sulfuric, citric, carbonic, boric, carboxylic, sulfonic, malic,phosphoric, succinic and acetic acids or combinations thereof), or bases(e.g., hydroxides such as those of Group 1 elements, ammonium, andorganic compounds; metal oxides such as those of Group 1 metals; andorganic and metal amines). Additives such as alcohols and polyethyleneglycol based compounds can be used to prevent freezing of the fluid.Additives such as surfactants, wetting agents and anti-foaming agents(e.g., glycols, polyglycols and polyols) can be used to control theliquid surface tension and reaction product viscosity to facilitate theflow of hydrogen gas and/or effluents. Additives such as porous fibers(e.g., polyvinyl alcohol and rayon fibers) can help maintain theporosity of a solid reactant component and facilitate even distributionof the reactant-containing fluid and/or the flow of hydrogen andeffluents.

In one embodiment a chemical hydride such as sodium borohydride (SBH) isone reactant, and water is another reactant. The chemical hydride can bea component of a liquid such as water. The chemical hydride and watercan react when they are exposed to a catalyst, an acid or heat in thereaction chamber. Alternatively, the chemical hydride can be stored as asolid in the reaction area, as essentially loose granules or powder orformed into a desired shape, for example. If an increased rate ofreaction between the chemical hydride and the water is desired, a solidacid, such as malic acid, can be mixed with the chemical hydride, oracid can be added to the water. A chemical hydride can be formed into amass, such as a block, tablet or pellet, to reduce the amount ofunreacted chemical hydride contained in the effluent that exits thereaction area. As used below, “pellet” refers to a mass of any suitableshape or size into which a solid reactant and other optional ingredientsare formed. The pellet should be shaped so that it will provide a largecontact surface area between the solid and liquid reactants. In anexample, a mixture including about 50 to 65 weight percent SBH, about 30to 40 weight percent malic acid and about 1 to 5 weight percentpolyethylene glycol can be pressed into a pellet. Optionally, up toabout 3 weight percent surfactant (anti-foaming agent), up to about 3weight percent silica (anti-caking agent) and/or up to about 3 weightpercent powder processing rheology aids can be included. The density ofthe pellet can be adjusted, depending in part on the desired volume ofhydrogen and the maximum rate at which hydrogen is to be produced. Ahigh density is desired to produce a large amount of hydrogen from agiven volume, but high porosity enables a higher rate of hydrogengeneration. On the other hand, if the pellet is too porous, unreactedSBH can more easily break away and be flushed from the reaction area aspart of the effluent. One or more pellets of this solid reactantcomposition can be used in the hydrogen generator, depending on thedesired volume of hydrogen to be produced by the hydrogen generator. Theratio of water to SBH in the hydrogen generator can be varied, based inpart on the desired amount of hydrogen and the desired rate of hydrogenproduction. If the ratio is too low, the SBH utilization can be too low,and if the ratio is too high, the amount of hydrogen produced can be toolow because there is insufficient volume available in the hydrogengenerator for the amount of SBH that is needed.

It may be desirable to provide for cooling of the hydrogen generatorduring use, since the hydrogen generation reactions can produce heat.The housing may be designed to provide coolant channels. In oneembodiment standoff ribs can be provided on one or more externalsurfaces of the housing and/or interfacial surfaces with the fuel cellsystem or device in or on which the hydrogen generator is installed ormounted for use. In another embodiment the hydrogen generator caninclude an external jacket around the housing, with coolant channelsbetween the housing and external jacket. Any suitable coolant can beused, such as water or air. The coolant can flow by convection or byother means such as pumping or blowing. Materials can be selected and/orstructures, such as fins, can be added to the hydrogen generator tofacilitate heat transfer.

It may also be desirable to provide means for heating the hydrogengenerator, particularly at startup and/or during operation at lowtemperatures.

The hydrogen generator can include other components, such as controlsystem components for controlling the rate of hydrogen generation (e.g.,pressure and temperature monitoring components, valves, timers, etc.),safety components such as pressure relief vents, thermal managementcomponents, electronic components, and so on. Some components used inthe operation of the hydrogen generator can be located externally ratherthan being part of the hydrogen generator itself, making more spaceavailable within the hydrogen generator and reducing the cost byallowing the same components to be reused even though the hydrogengenerator is replaced.

The hydrogen generator can be disposable or refillable. For a refillablehydrogen generator, reactant filling ports can be included in thehousing, or fresh reactants can be loaded by opening the housing andreplacing containers of reactants. If an external pump is used to pumpliquid from the reservoir to the reaction area, an external connectionthat functions as a fluid reactant composition outlet to the pump canalso be used to refill the hydrogen generator with fresh liquid. Fillingports can also be advantageous when assembling a new hydrogen generator,whether it is disposable or refillable. If the hydrogen generator isdisposable, it can be advantageous to dispose components with lifeexpectancies greater than that of the hydrogen generator externally,such as in a fuel cell system or an electric appliance, especially whenthose components are expensive.

The liquid reservoir, reaction area, byproduct containment area andhydrogen containment area can be arranged in many different ways. Byarranging the byproduct containment area in a volume exchangingrelationship with one or both of the liquid reservoir and the reactionarea, the hydrogen generator can be more volume efficient and provide agreater amount of hydrogen per unit of volume of the hydrogen generator.Other considerations in arranging the components of the hydrogengenerator include thermal management (adequate heat for the desiredreaction rate and dissipation of heat generated by the reactions), thedesired locations of external connections (e.g., for hydrogen gas,liquid flow to and from an external pump), any necessary electricalconnections (e.g., for pressure and temperature monitoring and controlof fluid reactant flow rate), and ease of assembly.

Liquid containing a reactant is initially disposed in the liquidreservoir, which is bounded by a container. The container is made of aliquid impermeable material that is stable in the environment of thehydrogen generator (e.g., nonreactive with the contents of thereservoir). It can be either gas impermeable or gas permeable. A gaspermeable container can allow small amounts of hydrogen that may beformed within the liquid reservoir to escape. While the container couldbe a rigid container, a flexible container can become smaller (e.g., bycollapsing and/or contracting) as liquid is transferred out of thereservoir, so that space initially occupied by the reservoir can be madeavailable to an enlarging byproduct containment area. Examples of typesof flexible containers include containers with walls having accordionfolds, similar to a bellows; elastic containers that can stretch andcontract in response to changes in pressure like a balloon; andcontainers made of nonelastic materials that are not rigid but also donot stretch or contract to a great extent. Examples of flexible, filmsinclude polyethylene, polypropylene, polyvinylchloride, rubber, latex,silicone, nylon, Viton, polyurethane, neoprene, buna-N,polytetrafluoroethylene, expanded polytetrafluoroethylene,perfluoroelastomers, and fluorosilicone. Of these, rubber, latex,silicone, Viton, neoprene, buna-N and perfluoroelastomers are generallyelastic, as well as some polyvinylchloride and polyurethane films. Allof these films are hydrogen permeable to at least some degree, and mostare also generally liquid impermeable.

Liquid is transferred from the liquid reservoir to the reaction area.This can be done by one or more methods, including pressurizing thecontainer and/or the liquid within the container, wicking the liquid tothe reaction area and pumping the liquid. Pressure can be applied to theliquid or the liquid reactant container with a pressurized gas within oroutside the liquid reactant container or a biasing component such as aspring, compressed rubber or compressed foam for example. Liquid can bewicked from one area to another by a material that is readily wetted byand can transport the liquid by capillary action. The wicking materialcan extend along the entire liquid transfer path from within the liquidreservoir to within the reaction area or along only a portion of theliquid transfer path. A wicking component can be made of, coated orlined with, or filled with the wicking material. When the liquidincludes water, the wicking material can be a hydrophilic material suchas cotton, polyester or nylon, for example. Liquid can also be pumpedfrom the liquid reservoir to the reaction area using one or more pumps,which can be within or outside the hydrogen generator. Pumps arepreferably as small as possible while being able to pump sufficientliquid for the hydrogen generator to supply hydrogen gas at the maximumdesired rate. Locating pumps outside the hydrogen generator can allowmore space for reactants within the housing and can reduce the totalcost of a system with a disposable hydrogen generator. Examples of typesof pumps that may be suitable include rotary, screw, piston, diaphragm,peristaltic pumps, centrifugal, radial flow, axial flow and impedancepumps.

The reaction area can be an area in which reactants come in contact witheach other and/or with one or more reaction initiators such ascatalysts, acid or heat, and in which the reactants react to producehydrogen gas. As described above, all reactants may be included in oneor more liquids, or one or more solid reactants can be initially storedwithin the reaction area. The reaction area is an area within thereaction container, which can be a rigid or flexible container, asdescribed above for the liquid reactant container. With a flexiblecontainer the reaction area can participate in volume exchange with thebyproduct containment area by becoming smaller as reactants initiallystored within the reaction area are consumed. In addition, force appliedto the reactants in a reaction area within a flexible container canfacilitate good contact among reactants, reaction initiators andadditives, as well as help to move hydrogen gas and byproducts out ofthe reaction area toward the byproduct containment area, to achieve goodreactant utilization and hydrogen generation efficiency. In anembodiment, a solid reactant and optional additives are formed into asolid pellet that is initially disposed within the reaction area; aliquid including another reactant is transported to the reaction area,where it contacts the pellet, and a hydrogen generating reaction occurs.The reaction container in this embodiment can include an elasticmaterial that is initially stretched and applies force against thepellet to minimize space between the pellet where liquid reactant andbyproducts can accumulate. An elastic, flexible or non-elastic containercan be wrapped with an elastic material (e.g., an elastic film or band)or biased by one or more springs or other biasing members.

A liquid disperser can be used to improve distribution of liquid withinthe reaction area. For example, the liquid disperser can includefeatures such as one or more nozzles (e.g., spray nozzles), a tubularstructure with one or multiple branches and multiple liquid outlets, awicking member that can wick liquid over a large surface in contact withanother reactant in the reaction area, and combinations thereof.

The reaction container includes an outlet from which hydrogen gas andbyproducts (gases, fluids and solids) can exit the reaction area. Theoutlet can be just an opening in the reaction chamber, an additionalstructure incorporated into the container wall, a screen or filter toretain large solid particles within the reaction area, a valve or acombination thereof.

Unreacted reactants can be carried out of the reaction area by hydrogengas and byproducts exiting therefrom. These reactants may continue toreact after leaving the reaction area, e.g., in the byproductcontainment area. This produces additional hydrogen gas and contributesto the total volume of hydrogen that the hydrogen generator produces. Inorder to maximize the possible hydrogen output, it can be advantageousto transport some of the liquid from the liquid reservoir to an areaoutside the reaction area (e.g., to a portion of the byproductcontainment area or an intermediate area between the reaction andbyproduct containment areas). This can be especially beneficial whenunreacted reactants include solid particles, particularly if there isinsufficient unreacted liquid reactant present.

Hydrogen gas and byproducts from the reaction area enter the byproductcontainment area, which has a byproduct container made of a materialthat is liquid impermeable but permeable to at least hydrogen gas.Preferably the container is flexible so that it initially encloses asmall volume but expands to contain byproducts. The container can besimilar to those described above for the reaction area and the liquidreservoir, as long as it is liquid impermeable and hydrogen permeable.Preferably the container has a sufficient hydrogen permeability to allowhydrogen gas to enter the hydrogen containment area at a rate adequateto meet the hydrogen gas demand. Because liquids and solids will notpermeate the container, the container separates hydrogen gas fromliquids and solids that enter the byproduct containment area. Thebyproduct container can have a large surface area to both provide ahigher rate of hydrogen gas entry into the hydrogen containment area.The large surface area is also useful in preventing blockage of hydrogentransmission through the container due to accumulation of solids on theinner surface of the byproduct container. This is especiallyadvantageous when byproduct and/or unreacted reactants can form a crustthat can tend to restrict the transmission of hydrogen gas. Movement ofa flexible container can also serve to fracture and/or strip accumulatedsolids as the byproduct containment area enlarges. It can also beadvantageous for the byproduct container to be elastic to furthercontribute to breaking and removing solids from the surface of thecontainer. The initial size of the byproduct containment area can beestablished based on factors such as the initial volume of liquid in theliquid reservoir, the initial volume of reactants and additives in thereaction area and the volume of byproducts that may be produced (thevolume of the byproducts may be greater than the combined volume of thereactants).

To reduce the accumulation of solids on the inner surface of thebyproduct container, one or more additional filters can be disposed inthe byproduct containment area to remove a portion of the solids as theeffluent from the reaction area passes through the byproduct containmentarea to the surface of the container. A series of filters can be usedand arranged so the larger particles will be removed first. For example,the general flow path through the byproduct containment area may bethrough a coarser, more porous filter first, followed by successivelyfiner, less porous filters, to prevent clogging of the filters. Filterswith high stability, low reactivity with the effluent from the reactionarea are preferred. Some types of filters can also be initiallycompressed and expand as the byproduct containment area expands,contributing to the volume efficiency of the hydrogen generator or beingless resistant to clogging. Filters can be made of materials such asnylon, polytetrafluoroethylene, polyolefins, carbon and other materials.

Hydrogen gas that passes through the byproduct container enters thehydrogen containment area, which is sealed within a hydrogen gascontainer made of a hydrogen impermeable material. The hydrogen gascontainer serves as a reservoir for hydrogen gas that is generated butnot yet released from the hydrogen generator. This provides a bufferthat can initially contain a small amount of hydrogen gas that can beprovided before sufficient hydrogen has been produced during initial useand following subsequent startups. The hydrogen containment area canalso contain hydrogen gas produced during periods when the release ofhydrogen gas is halted, between stopping the transfer of liquid to thereaction area and the time at which reactants already in the reactionarea (and byproduct containment area) are consumed and generation ofhydrogen gas is halted. The size of the hydrogen containment area can beestablished based on factors such as the types of reactants used, therate of hydrogen gas production, the volume of byproducts produced, therate at which hydrogen gas is to be supplied and the amount of hydrogengas desired to be available at startups.

The hydrogen gas container is impermeable with respect to hydrogen gas,thereby preventing leakage of hydrogen gas through the hydrogengenerator housing, without requiring the walls of the housing to beimpermeable with respect to hydrogen gas and the housing to behermetically sealed. The internal hydrogen gas container can provide aredundant gas seal, adding to the safety and reliability of the hydrogengenerator. Hydrogen impermeable materials include metallized polymericfilms and metal-polymeric composite films such as laminates withpolymeric and metal layers. Examples of suitable polymeric films includepolyethyleneterephalate, polyvinylchloride, polyethylene, polycarbonate,polyimide, polypropylene and polyamide. Examples of suitable metalsinclude aluminum, chromium, nickel and gold. An adhesive can be includedon surfaces of the material that are sealed to make a sealed container.The entire inner surface can be a layer of material that can function asan adhesive. For example, polyethylene can be heat sealed. A preferredtype of material is a laminate including three or more layers, with themiddle layer being a metal and the outer layer being polymeric layers.

The hydrogen gas container encloses both the byproduct containment areaand the reaction area. All hydrogen gas produced in the reaction area ordownstream therefrom passes through the hydrogen gas container so thehydrogen gas is effectively separated from liquids and solids. Theliquid reservoir can be disposed outside or within the hydrogen gascontainer. It can be advantageous for the liquid reservoir to be withinthe hydrogen gas container, especially if the liquid contains a hydrogensource that can react during periods of nonuse to produce small amountsof hydrogen gas, since this hydrogen gas can also be captured within thehydrogen gas container, thereby maximizing the hydrogen gas output fromthe hydrogen generator.

Hydrogen gas exits the hydrogen containment area through an outlet. Thehydrogen gas container can be sealed to the outlet. The outlet caninclude one or more valves to seal the hydrogen generator when it is notproviding hydrogen and to allow hydrogen to exit the hydrogen generatorwhen desired.

Some reactants may contain or produce gaseous byproducts, and it may bedesirable to remove these gases, especially if they can damage thehydrogen consuming apparatus being supplied with hydrogen. This mayrequire additional filters, etc., either within the hydrogen generatoror elsewhere in the system.

The hydrogen generator can include other features, such as a pressurerelief mechanism to safely release excessive internal pressure due to anabnormal condition.

The generation of hydrogen gas can be started and stopped by startingand stopping the transfer of liquid from the liquid reservoir to thereaction area. This can be done manually (e.g., with a manually operatedswitch) or automatically. Automatic operation can be accomplished with acontrol system, which can be disposed within or outside the hydrogengenerator, or a combination thereof. Control can be based on the demandfor hydrogen, e.g., for a fuel cell system. In a fuel cell system,demand can be determined by monitoring and/or communicating with thefuel cell stack, an electric appliance being powered by the stack, abattery being charged by the stack, and so on.

The hydrogen generator can include thermal controls. For example, heatcan be applied to assist in initiating the reaction, particularly atstartup and when the ambient temperature is low. The hydrogen generatorcan be cooled if necessary to remove excess heat generated in thehydrogen generating reaction. Heating and cooling can be done by avariety of methods, including air convection, circulation of heating andcooling fluids, electrical heaters, and so on. A thermal control systemcan also include temperature monitors, etc. The thermal control systemmay be disposed within or outside the hydrogen generator, or acombination.

A hydrogen generator according to an embodiment is shown in FIGS. 1 and2. The embodiment shown can be further modified according to the abovedescription, to include variations in such things as the types andinitial locations of reactants; the size, shape and relative locationsof individual components; and the incorporation of optional features andcomponents into the hydrogen generator. FIG. 1 is a schematicrepresentation of a hydrogen generator 10 in an initial condition,before use, and FIG. 2 is a schematic representation of the hydrogengenerator 10 after at least partial use. The hydrogen generator 10includes a housing 12. Within the housing 12 is a reaction area 22within a reaction container 20 and a liquid reservoir 24 within a liquidreactant container 20. A liquid containing a reactant such as water isinitially contained in the liquid reservoir 24. The liquid can alsocontain another reactant, such as a chemical hydride dissolved therein,in which case reaction between the water and the chemical hydride isinitiated within the reaction area 22 after a quantity of the liquid istransferred from the liquid reservoir 24 to the reaction area 22.Alternatively, another reactant can be contained in a second liquid,initially contained within either the reaction area 22 or a secondliquid reservoir (not shown) from which it is transferred to thereaction area 22; or a solid containing a reactant can be initiallycontained within the reaction area 22, in the form of one or morepellets for example. Liquid is transferred from the liquid reservoir 24to the reaction area 22, where reactants react to produce hydrogen gasand byproducts. Liquid can be transferred from the liquid reservoir 24via an internal flow path (not shown) or via an external flow path fromthe liquid reservoir 24, through a liquid reactant outlet 30 to aportion of the flow path outside the hydrogen generator 10, back intothe hydrogen generator 10 through a liquid reactant inlet 32 and intothe reaction area 22. The liquid can be dispersed within the reactionarea 22 by a liquid disperser 34. The reactants react within thereaction area 22, and hydrogen gas and reaction byproducts that areproduced exit the reaction area 22 through a reaction area outlet 36 andenter a byproduct containment area 26 within a byproduct container 16.The byproduct container 16 is liquid impermeable and hydrogen permeableso liquids and solids remain within the byproduct containment area 26,while hydrogen gas passes through the byproduct container 16 into thehydrogen containment area 28. Hydrogen gas is released from the hydrogengenerator 10 as needed, through a hydrogen gas outlet 38.

The byproduct containment area 26 can be in a volume exchangingrelationship with one or both of the liquid reservoir 24 and thereaction area 22, as shown in FIG. 2. As the hydrogen generator 10 isused, liquid is transferred from the liquid reservoir 24 and hydrogengas and byproducts exit the reaction area 22. Flexible containers 20 and18 can allow these areas to become smaller in volume, with a concurrentincrease in the volume of the byproduct containment area 26. Initiallythe byproduct containment area 26 can be very small, or it can be largerto accommodate a larger anticipated volume of byproducts. The byproductcontainment area 26 can be in a volume exchanging relationship with thehydrogen containment area 28, if, for example, the byproduct container16 is flexible and able to move in response to changes in the relativepressures applied by the contents of the byproduct containment area 26and the hydrogen containment area 28.

All references cited herein are expressly incorporated herein byreference in their entireties. To the extent publications and patents orpatent applications incorporated by reference contradict the disclosurecontained in the present specification, the present specification isintended to supersede and/or take precedence over any such contradictorymaterial.

It will be understood by those who practice the invention and thoseskilled in the art that various modifications and improvements may bemade to the invention without departing from the spirit of the disclosedconcept. The scope of protection afforded is to be determined by theclaims and by the breadth of interpretation allowed by law.

The invention claimed is:
 1. A hydrogen generator comprising: a housing;a liquid reservoir within the housing and comprising a liquid reactantcontainer, made of a liquid impermeable material, and containing aliquid comprising a first reactant; a reaction area within the housingand comprising a reaction container, made of a liquid impermeablematerial, and within which the first reactant reacts to produce hydrogengas and byproducts; a byproduct containment area within the housing andcomprising a flexible byproduct container, made of a hydrogen permeable,liquid impermeable material through which solids and liquids cannot passbut through which hydrogen gas can pass; a hydrogen containment areawithin the housing and comprising a flexible hydrogen gas container,made of a hydrogen impermeable material, and configured to containhydrogen gas from the byproduct containment area; and a hydrogen outletfrom the hydrogen containment area through the housing; wherein thebyproduct containment area is in a volume exchanging relationship withat least one of the liquid reservoir and the reaction area; and whereinthe hydrogen containment area and the byproduct containment area beingseparated by a common wall comprising the hydrogen permeable, liquidimpermeable material so as to allow the passage of hydrogen from thebyproduct containment area to the hydrogen containment area.
 2. Thehydrogen generator according to claim 1, wherein the byproduct containermaterial is an elastic material, capable of stretching and contracting.3. The hydrogen generator according to claim 1, wherein the byproductcontainer material comprises a fluoropolymer.
 4. The hydrogen generatoraccording to claim 3, wherein the fluoropolymer comprises an expandedfluoropolymer.
 5. The hydrogen generator according to claim 4, whereinthe fluoropolymer comprises polytetrafluoroethylene or apolytetrafluoroethylene derivative.
 6. The hydrogen generator accordingto claim 1, wherein the hydrogen containment container materialcomprises a metallized polymer film or a metal-polymer composite film.7. The hydrogen generator according to claim 1, wherein a catalystconfigured to catalyze the reaction of the first reactant is initiallycontained within the reaction area.
 8. The hydrogen generator accordingto claim 1, wherein a second reactant is initially contained within thereaction area.
 9. The hydrogen generator according to claim 8, whereinthe second reactant comprises a chemical hydride.
 10. The hydrogengenerator according to claim 8, wherein the second reactant is a solid.11. The hydrogen generator according to claim 10, wherein a solid pelletcomprises the second reactant.
 12. The hydrogen generator according toclaim 11, wherein the solid pellet further comprises a binder.
 13. Thehydrogen generator according to claim 8, wherein the hydrogen generatorcomprises an accelerant that is capable of providing an increased rateof reaction.
 14. The hydrogen generator according to claim 13, whereinthe accelerant comprises an acid.
 15. The hydrogen generator accordingto claim 1, wherein the reaction container comprises an outlet throughwhich hydrogen gas and byproducts can exit to the product containmentarea.
 16. The hydrogen generator according to claim 1, wherein thehydrogen generator further comprises a pump configured to pump theliquid from the liquid reservoir to the reaction area.
 17. The hydrogengenerator according to claim 16, wherein the pump is disposed within thehydrogen generator.
 18. The hydrogen generator according to claim 1,wherein a liquid dispersion device is disposed within the reactionchamber.
 19. A fuel cell system comprising a fuel cell stack and ahydrogen generator according to claim
 1. 20. The fuel cell systemaccording to claim 10, wherein the hydrogen generator is removable fromthe rest of the fuel cell system.
 21. A hydrogen generator of claim 1,wherein the reaction area is contained within the byproduct containmentarea, the hydrogen containment area, or both the byproduct and hydrogencontainment areas.
 22. A hydrogen generator of claim 8, wherein thesecond reactant comprises a metal hydride.
 23. A hydrogen generator ofclaim 8, wherein the second reactant comprises sodium borohydride.
 24. Ahydrogen generator comprising: a housing; a liquid reservoir within thehousing and comprising a liquid reactant container, made of a liquidimpermeable material, and containing a liquid comprising a firstreactant; a reaction area within the housing and comprising a reactioncontainer, made of a liquid impermeable material, and within which thefirst reactant reacts to produce hydrogen gas and byproducts; abyproduct containment area within the housing and comprising a flexiblebyproduct container, made of a hydrogen permeable, liquid impermeablematerial through which solids and liquids cannot pass but through whichhydrogen gas can pass; a hydrogen containment area within the housingand comprising a flexible hydrogen gas container, made of a hydrogenimpermeable material, and configured to contain hydrogen gas from thebyproduct containment area; and a hydrogen outlet from the hydrogencontainment area through the housing; wherein the byproduct containmentarea is in a volume exchanging relationship with at least one of theliquid reservoir and the reaction area; wherein the flexible hydrogengas container encloses both the flexible byproduct container and thereaction container.
 25. The hydrogen generator of claim 24, wherein thebyproduct containment area contains the liquid reservoir and thereaction area; and the hydrogen containment area contains the byproductcontainment area.